Roll for pressure fusing toner at elevated temperatures

ABSTRACT

A silicone rubber roll for pressure fusing of electrostatically produced and toned images at elevated temperatures. The roll inherently prevents offset of the image by supplying a release material to the surface of the roll. When the release material is depleted the roll can be restored by impregnation with silicone oil.

United States Patent 1191 Artl 1 May 8, 1973 [54] ROLL FOR PRESSURE FUSING TONER [56] References Cited I AT ELEVATED TEMPERATURES UNITED STATES PATENTS 2,639,519 S 1953 P lk t l ..29 l32X 1 lnvemo" Kenneth Williams, 3,225,419 l2l965 M11101; al. .29/132 [73] Assignee: Addressograph-Multigraph Cor Primary Examiner-Alfred Guest pomfion Cleveland, Ohio Attorney-Russell L. Root and Ray S. Pyle 22 Filed: May 2 6, 19 71 [57] ABSTRACT A silicone rubber roll for pressure fusing of electro- [21] Appl. No.: 145,563 statically produced and toned images at elevated temperatures. The roll inherently prevents offset of the 2 image by supplying a release material to the surface of [52] U 8 Cl 29/132 the roll. When the release material is depleted the roll [51] 31,08 can be restored y impregnation with silicone oil. [58] Field of Search; .29/132, 129.5 E 2 Claims, No Drawings ROLL FOR PRESSURE FUSING TONER AT ELEVATED TEMPERATURES BACKGROUND OF THE INVENTION This invention relates generally to rolls utilized for pressure fusing toners at elevated temperatures, and more particularly to a roll which will prevent offsetting of the toner onto the roll during the fusing operation.

One of the conventional practices of fusing or fixing toner in the electrostatic image forming process is'by the concomitant application of heat and pressure. This is often done by providing a roll pair maintained in pressure contact through which the article having the applied but unfused toner is passed. Heat is applied conventionally by heating one orboth of the rolls. The fusing of the toner takes place when the proper combination of heat, pressure, and contact time are provided. The balancing of these parameters is well known in the art and will vary according to many factors and for each particular situation must be independently determined.

One of the problems encountered in the pressure fusing technique is the propensity of the toner to offset or adhere to the roll which comes in contact herewith as the article is padded between the rolls. For example, conventional rolls having an outer Teflon coating, which has been one of the more conventional prior art configurations of a roll for pressure fusing, have a very strong tendency to retain the toner thereon during a pressure fusing operation. To overcome this tendency for the roll to pick up the toner some type of release fluid is continuously applied to the surface of the roll to prevent such offset. It has been found that silicone fluids, commonly known as silicone oils, are especially well adapted for this purpose in that they not only tend to prevent offsetting of the toner onto the roll but they also provide desirable lubrication. However, the constant application of the fluid requires a separate fluid reservoir and fluid applying means as well as metering and control to maintain the proper amount of fluid on the roll. This requires not only additional equipment at an increased expense, but it also affords an increased propensity toward malfunctioning contributing toward down time and expensive maintenance.

SUMMARY OF THE INVENTION According to the present invention a roll for pressure DESCRIPTION OF THE PREFERRED EMBODIMENT According to the present invention a roll for pressure fusing a toner at elevated temperatures is provided which roll has an outer layer of material of an elastomeric material which will be provided at the surface thereof from within itself a release material for the prevention of offsetting or sticking of the toner to the roll as the roll rotates in contact with the toner. One

convenient way of forming such a roll is providing such an outer layer of elastomeric material wound onto a central tube into which tube a heating element can be inserted.

In the preferred embodiment the outer layer of elastomeric material is an elastomeric silicone compound commonly referred to as silicone rubber. The specific type and composition of the silicone rubber which is selected for the application as well as the thickness thereof may vary with different specific applications of pressure fusing at elevated temperatures. Such variables as hardness of the material, thermal conductivity, roll pressure, roll speed, and heat input all have to be balanced in a manner to provide the most effective fusing operation. The selection and balancing of the variables is well known in the art and affect the selection of the particular silicone rubber which is to be utilized.

Several satisfactory silicone rubbers include Silastic 735 black RTV and Silastic 732 RTV, both manufactured by Dow Coming, and 106 RTV Silicone Rubber and RTV Silicone Rubber, both manufactured by General Electric. These are cited by way of example as silicone rubbers that are satisfactory but it is to be understood that this invention is not limited to the use of these specific elastomerics.

The manufacture of the rolls of the present invention is guite simple compared to the more complex manufacturing required of the prior art Teflon rolls. In the preferred embodiment the roll of the present invention is manufactured by first providing a hollow metallic tube such as copper, alluminum, etc., then coating the tube with a primer and finally coating the primed tube to the desired thickness thereon with the raw silicone rubber. The rubber is then cured. This is the entire process.

In contradistinction the manufacturing of a Teflon coated roll requires that first the copper tube be machined and provided with a matte finish. The tube with the matte finish is then nickel plated which is followed by successive coatings of Teflon primer and finally a coating of the Teflon itself. Thus, not only is a superior roll provided, but also a much simpler manufacturing technique is required to provide such roll.

As an example of the effectiveness of a fusing roll according to this invention, an aluminum tube having 3.5 inches OD and 3.4 inches ID was primed and coated to a thickness of approximately 0.015 inch with 90 RTV Silicone Rubber manufactured by General Electric. The coating was cured and the roll was used in a test operation in combination with a pressure roll formed from Dow Corning Silicone Rubber 095-033 secured on a 1% inch steel shaft. Heat was supplied to the system by means of a 750 watt quartz iodine lamp disposed within the aluminum tube of the fusing roll. The tube rotated around the lamp at a roll surface speed of 50 inches per second. The surface temperature of the roll was controlled at between 400 and 450 fahrenheit and a pressure of approximately 21 pounds per lineal inch was maintained.

Toned electrostatic images on standard 9.5 inch envelopes were fed through the roll pair. Over 300,000 of these images were fused in the test before any offsetting or sticking of the toner to the heated roll was apparent. Thus a rather large number of images can be fused with a single roll without the necessity of applying any fluid to the operation as the fusing continues.

The exact reason for the outstanding performance of silicone rubbers in preventing offsetting is not completely understood. However, the silicone rubber, during its use in pressure fusing at elevated temperatures under pressure, provides at the surface thereof from within a release compound which effectively presents the offsettting of the toner onto the roll. This inherent prevention of offsetting continues until the release compound is depleted to such an extent that it no longer is brought to the surface in a manner to be effective to prevent offsetting.

At this point the roll with the depleted release compound can be discarded and a new roll inserted if it is so desired. However, it has been found that the release characteristics of the roll can be restored by impregnating the roll with a silicone liquid commonly known as silicone oil.

In the above described test after offsetting had become apparent, the silicone rubber outer material of the roll was coated with SF 96 (1000) Silicone Fluid a dimethyl polysiloxane, manufactured by General Electric, commonly known as silicone oil and the material allowed to soak into the silicone rubber overnight. This roll was again resued under the same test conditions, and fushed approximately 200,000 additional images before offsetting again became apparent. Treatments thereafter with SF 96 (1000) silicone oil again yielded an additional approximately 200,000 fused images before offsetting again became apparent. Treatments thereafter with SF 96 (1000) silicone oil again yielded an additional approximately 200,000 fused images before offsetting occurred. This process of impregnating the material appeared to be necessary approximately every 200,000 images thereafter with the roll restored to its release characteristics each time. Thus, not only is a roll provided which inherently provides a release material to surface thereof from within for a substantial number of operations, but also a roll is provided which after the release composition has been depleted from within it may be restored by treatment with a suitable fluid.

It is to be understood that the above fusing with General Electric RTV Silicone is merely illustrative of material which can be used and not limiting. For example, tests with the previously enumerated. silicone rubber material showed that they also performed satisfactorily for pressure fusing.

What is claimed is:

l. A roll for pressure fusing toned electrostatic images at elevated temperatures having improved resistance to toner ofiset comprising a cylindrical member, a working surface of cured silicone rubber on said cylinder and a coating consisting essentially of sil- 

2. The roll as defined in claim 1 wherein said silicone oil is a dimethyl polysiloxane. 